Monte Carlo Methods for Core Safety Analysis: Design of Instrumentation for Monitoring PWR Core Degradation in case of a Severe Accident

Support to IRSN in safety evaluations in PWR’s has proceeded. The final results were supplied in early March, 2015. Some further calculations were made to analyse the system in the light of the results already obtained. Variations on the basic model were: a 239Pu fission spectrum as source; a homogenous fission source in the core (for comparison purposes with results obtained at IRSN). The decoupled approach with the patch to read the pin-by-pin fission source and the DSA variance reduction patch in the second, fixed source, part of the calculation has performed satisfactorily. All the requested neutron and gamma responses have been generated with a sufficiently small statistical error and within the project deadlines. The innovative, single-calculation approach is currently being tested on this problem. Current indications are that the fundamental mode must be verified with an analogue calculation to ensure that the error estimates on the ex-core responses are correct.